Tel Aviv—Amid heavy international pressure on the issue, domestic political support for Israel’s economic blockade of the Gaza Strip border passages has badly frayed.

Once confined largely to the Israeli left, criticism of a policy that banned basic goods such as fresh meat, margarine and plaster has spread to security hawks who acknowledge the closure is not serving its original policy goal of weakening Hamas. That may make it easier politically for the government to make concessions on a blockade that, until now, has enjoyed widespread popular support.

As Prime Minister Benjamin Netanyahu openly courts pro-settler nationalists in his bid for re-election May 17, some of his biggest American supporters on the ideological right are either abandoning him or saying they are open to other candidates.